Such methods are used in the manufacture of steel. The liquid steel is supplied by a steelworks. The secondary metallurgy is then performed in a ladle furnace arranged upstream of a thin-strip continuous casting machine. In addition, certain secondary metallurgical equipment is provided in/on the ladle furnace for metallurgical treatment of the liquid steel. This equipment can be used to perform precise analyses of the melt and also for precise thermal conditioning of the melt. The liquid steel is treated in the ladle furnace by adding alloying agents, slag formers, reduction agents, desulfurization agents, etc., where these additives are added automatically or manually. In addition, the slag can be treated by adding oxygen or by rinsing with an inert gas such as argon. The liquid steel can be stirred electromagnetically in the ladle, and electrical energy can also be supplied to it via carbon electrodes. The arc passing from the electrodes to the melt causes the alloying elements to melt and enables the thermal conditioning of the melt.
In order to manufacture from the melt a specific steel quality having defined material properties such as strength, toughness, hardness, corrosion resistance etc., it is necessary to add metal and non-metal alloying elements and additives. Mathematical models are used for this purpose, said models calculating from a latest analysis of the melt the material composition of the required alloying elements and additives in order to obtain a very specific steel quality. The proportions of the metal and non-metal elements are thereby set in a defined band. Additional strength formulae that take account of the interactions between the alloying elements and additives in the melt are applied in a quality center in order to assess the expected material properties. These formulae are mainly empirical. In conventional works comprising steelworks, ladle furnace and continuous casting machine, such calculations of the interactions of the additives and alloying elements are at best performed offline in quality centers. The strength formulae and empirical formulae cited in the literature are simplified models for the complex interactions of the alloying elements and additions that influence the material properties of the cast steel.
Thin-strip continuous casting machines mainly manufacture steel strips having a strip thickness of up to 10 mm. The melt is conditioned following an analysis in a similar way to in conventional machines. It has been found, however, that in thin-strip continuous casting machines, the castability of the liquid steel is far more problematic than in conventional casting machines, e.g. in continuous casting machines for slabs.
Liquid steel is designated as uncastable if the cast strip cracks e.g. when casting in the thin-strip continuous casting machine, the cast material exhibits surface defects or structural faults of a general nature and it causes plant breakdowns as a result of the uncastable liquid steel e.g. sticking to the casting rollers etc. Until now, attempts to solve these problems with the castability have largely been made in the thin-strip continuous casting machine itself. These attempts were only partially successful, however, because many melts proved uncastable.